Counterbalance mechanism



P 1, 1964 c. T. BRIGGS, JR., ETAL 3,146,825

COUNTERBALANCE MECHANISM Filed June 14, 1962 2 Sheets-Sheet l 6 3a L 5%: L 22 20 INVENTOR. CHARAE'S 77 BR/6G s, J'R.

.7019 I KEMPEL ATTORNEYS p 1, 1964 c. T. BRIGGS, JR. ETAL 3,146,825

COUNTERBALANCE MECHANISM 2 Sheets-Sheet 2 Filed June 14 1962 INVENTORS ATTOR/Vf/J United States Patent Office 3,146,825 COUNTERBALAN CE MECHANISM Charles T. Briggs, Jr., Royal Oak, and John J. Kempel, Pontiac, Mich., assignors to Berry Industries, Inc., a corporation of Michigan Filed June 14, 1962, Ser. No. 202,556 10 Claims. (Cl. 160-191) This invention relates to apparatus for counterbalancing a vertically movable door, and more particularly to a prestressable spring counterbalancing mechanism for an overhead garage door which is supported by tracks for movement between a vertical closed position and a horizontal open position.

An object of the present invention is to provide an improved counterbalancing mechanism employing a spring which may be locked in a pre-stressed condition at the factory and safely shipped and installed in the pre-stressed condition to thereby reduce the effort and cost of installing the mechanism in the field.

Another object is to provide an improved spring counterbalancing mechanism of simple and rugged construe tion in which the spring is permanently confined to thereby prevent injury in the event of spring breakage.

Yet another object is to provide an improved counterbalanced overhead door arrangement in which the horizontal stresses imposed on the door supporting structure by the counterbalancing mechanism are greatly reduced, thereby eliminating the problem of the door binding in the tracks due to strain deflection of the supporting structure.

A further object is to provide an extension spring counterbalancing mechanism with improved means for adjusting the active length of the spring which is simple in construction, easy to adjust and suitable for use with various sizes of springs.

Other objects, features and advantages of the present invention will become apparent in the accompanying description and drawings in which:

FIG 1 is an elevational view of an overhead garage door counterbalanced in accordance with the present invention as viewed from inside the garage with the door down.

FIG. 2 is a diagrammatic fragmentary perspective view of the counterbalancing mechanism of the invention.

FIGS. 3 and 4 are enlarged fragmentary elevational and plan views respectively of the counterbalancing mechanism, FIG. 4 being a bottom view taken partially in horizontal section.

FIG. 5 is a side elevational view of the mechanism shown in FIGS. 3 and 4.

FIGS. 6 and 7 are sectional views taken respectively on the lines 6-6 and 7-7 of FIG. 3.

Referring in more detail to FIG. 1, there is shown a sectional overhead door 10 of conventional construction having rollers 12 which run in tracks 14 to guide and support the door for movement between the illustrated vertical, closed position thereof and a horizontal, open position thereof wherein the door is disposed overhead in wardly of and above the doorway. The improved door counterbalancing apparatus of the invention'is preferably installed in a horizontal arrangement over the doorway and includes three mounting brackets 16, 18 and 20 which are bolted to a header 22 defining the upper edge of the doorway. Brackets 18 and 20 support the opposite ends of a rigid shaft 24 which in turn supports a tension coil spring 26 which provides the counterbalancing force for door 10.

As shown diagrammatically in FIG. 2, spring 26 is operably connected to door 16 by a pair of cables 28 and 30, one for each side of the door, which are respectively attached at one end thereof to bracket 20 and at the other 3,146,825 Patented Sept. 1, 1964 end thereof to studs 32 and 34 connected to the bottom corners of door 10. Cable 28 extends upwardly along the left edge of the door, past a guide pulley 36 journalled on bracket 16 and then over a larger pulley 38 also journaled on bracket 16 but rotatable about an axis perpendicular to that of pulley 36. Cable 28 then extends horizontally to another guide pulley 40 mounted on bracket 18, then to a pulley 42 journalled on an axle 44, then back to a pulley 46 connected to one end of spring 26 and then to its connection with bracket 20. Cable 30 extends upwardly from stud 34 past a guide pulley '48 journalled on bracket 20, then over a pulley 50 journalled on axle 44 in perpendicular relation to pulley 48, then horizontally to a pulley 52 connected to the one end of spring 26 and then back to its connection with bracket 20. The end of spring 26 connected to pulleys 46 and 52 is movable along shaft 24 while the other end of the spring is afiixed to one end of shaft 24 by a clip 54.

With the above cable rigging arrangement the tension force exerted by spring 26 on pulleys 46 and 52 is divided equally between cables 28 and 30 so that uniform counterbalancing force is applied to the opposite side edges of door 10. When door 10 is raised, spring 26 contracts along shaft 24, pulling pulleys 46, 52 towards bracket 18 and causing equal take-up of cables 28, 30. Conversely, when door 10 is lowered its weight is transmitted via cables 28, 30 to spring 26 so that it extends to the fully stressed condition thereof shown in FIG. 1.

The structural features of the counterbalancing mechanism are more clearly shown in FIGS. 3-7. Shaft 24 is preferably a single length of pipe which extends coaxially completely through spring 26, with one end butting against the side of bracket 20 (FIGS. 3 and 4) and the other end extending through a rectangular opening 56 in the side of bracket 18. Axle 44 is supported at its ends in the back and front sides of bracket 20 and carries the weight of shaft 24 as well as half of the weight of the door 10. Bracket 18 merely supports half of the weight of shaft 24 plus the other parts of the mechanism adjacent bracket 18. Clip 54 comprises a generally U-shaped strap with bent back ends 58 and 60 (FIG. 4) which hook around the last two convolutions of spring 26 at the fixed end thereof. The U-shaped portion of clip 54 passes through opening 56 in bracket 18 and around the end of shaft 24 so that the tension of spring 26 is applied as a compressive force directly to the shaft. The tension force exerted by spring 26 on cables 28 and 30 is applied to the other end of shaft 24 by axle 44 and by a pair of cable books 64 and 66, the threaded ends of which pass through the side of bracket 20 and are adjustably secured thereto by nuts 68 and 70.

With this arrangement, the spring loads are taken entirely by shaft 24 and hence there is no horizontally di rected stress placed on the mounting bolts which secure brackets 18 and 20 to header 22. As a result there is less tendency for these brackets to work loose, and they may be economically made of relatively lightweight metal stampings. Moreover, since tracks 14 are preferably partially supported by a pair of channels 62 respectively connected to brackets 16 and 20 (FIGS. 1 and 3), the horizontal bracing of brackets 16 and 20 provided by shaft 24 also prevents door 10 from binding in tracks 14, a serious problem which otherwise would arise when the brackets worked loose and were pulled towards one another.

Another important feature of the present invention is the provision of means for locking the movable end of spring 26 to shaft 24 when the spring is fully extended so that the spring may be stretched at the factory and then shipped and installed with the spring in a pre-stressed condition. As shown in FIGS. 4 and 7, shaft 24 is provided with a pair of diametrically opposite holes 72 for receiving a headed locking pin 74 upwardly therethrough. Pin 74 also passes through a hole 75 in a crosspiece 76 so as to lock the crosspiece to shaft 24, and a cotter key 78 prevents pin 74 from falling out of holes 72, 75. Crosspiece 76 straddles shaft 24 and is secured by the axle bolts 84 and 86 of pulleys 46 and 52 to the inner arms of a pair of U-shaped straps 8t) and 82 which in turn hook around the two endmost convolutions of the movable end of spring 26. In addition to its locking function, crosspiece 76 links the two pulleys 46, 52 together so that they move as a unit and also serves as a sliding support for these pulleys and the movable end of spring 26. Preferably a lubricant impregnated felt pad 88 is glued to the underside of crosspiece 76 to reduce the noise and friction of the sliding engagement between crosspiece 76 and shaft 24.

The above locking structure is utilized to advantage by partially assembling and pre-stressing the counterbalance mechanism at the factory. The fixed end of spring 26 is secured via clip 54 to one end of shaft 24 and then the spring is stretched along shaft 24 until holes 75 and 72 register with one another, and then locking pin 74 is inserted upwardly through these holes and locked in place with cotter key 78. This securely locks spring 26 in its fully stressed condition so that it may be safely handled during shipping and installation while in this condition, thereby permitting connection of spring 26 to door 10 when it is down in the vertical closed position thereof. The cables 28, 30 are rigged over the pulleys and connected to the lowered door and hooks 64, 66 as previously described herein, and then key 78 is removed from pin 74. As nuts 68, 70 are tightened to even up the tension in cables 28, 30, the stress on pin 74 is relieved, thereby permitting it to drop out of crosspiece 76 and shaft 24. Thus the time and effort required for installation is greatly reduced, and the task of lifting the dead weight of door 10 and moving it to the overhead position is eliminated.

A further feature of the invention is the provision of an improved clamp structure for adjusting the active length of spring 26. As shown in FIGS. 3, 4, and 6, this clamp structure includes a curved plate 90 which overlies the convolutions of spring 26 adjacent the fixed end thereof. The left end of plate 90 abuts bracket 18 and has a pair of tabs 92 extending radially inwardly therefrom which are inserted through a pair of narrow slots 94 in the side of bracket 18 to thereby secure plate 90 against movement axially of spring 26. The upper surface of plate 90 is provided with a series of alternating recesses and ridges spaced axially and extending transversely thereof, preferably in the form of slots 86 and upwardly struck portions 98. A U-shaped rod 100 overlies plate 90 so as to straddle the spring when the center portion of rod 100 is received in a slot 96, and in this position the raised portions 98 on either side of rod 100 serve to retain it against movement axially of the plate. The dependent arms of rod 100 receive a curved cross piece 102 which is adjustably secured thereto by nuts 104. A conically pointed pin 106 is staked to crosspiece 102 and extends upwardly from the inner surface thereof so as to be wedged between a pair of adjacent spring convolutions when nuts 104 are tightened up.

With the above clamp structure, it is a simple matter to deadhead any desired number of the spring convolutions disposed between bracket 18 and the right end of plate 90 to thereby adjust the rate of spring 26 as needed for the particular installation. The tension exerted by spring 26 on plate 90 is then transmitted via tabs 92, bracket 18 and clip 54 to the end of shaft 24. Neither the spring nor the clamp structure need be rotated in adjusting the spring rate, and the clamp pieces 160, 102 and plate 90 may be used interchangeably with springs of different wire size It will now be apparent that the above-described prestressable counterbalancing mechanism of the invention provides signficant savings in manufacturing and installation costs, and when once installed is simple to adjust and reliable in operation. Due to the provision of shaft 24, the spring loads on the supporting structure are greatly reduced. In addition, the shaft and brackets 18 and 20 co-operate to support and confine spring 26 so that, should the spring break while under tension, it cannot be thrown loose and endanger occupants or contents of the building.

We claim:

1. A counterbalancing mechanism for use in balancing the weight of an overhead door supported for vertical movement to open and close a doorway in a structure, said counterbalancing mechanism comprising a rigid shaft, mounting means connected to the shaft for fixably supporting said shaft on said structure, a tension coil spring encircling said shaft between said mounting means and having one end thereof fixed to said shaft and the other end thereof movable along said shaft in the normal operating condition of said mechanism, means connected to said movable end of said spring adapted for operably conmeeting said spring to the door such that closing and opening movement of the door respectively causes said spring to axially extend and contract along said shaft to thereby counterbalance the door, and means detachably connecting the movable end of said spring to said shaft at a predetermined point therealong such that said spring is axially extended to thereby prestress said spring to facilitate connection thereof with the door, said means connected to said movable end of said spring comprising a pair of generally U-shaped straps disposed on opposite sides of said shaft and hooked through the associated side of said spring between a pair of convolutions thereof so as to engage said spring adjacent the movable end thereof, said straps each having a pair of arms extending beyond the movable end of said spring, first and second pulleys connected to and journalled respectively between said arms of said straps and means connected to said straps and extending therebetween transversely to said shaft, said last-mentioned means and said shaft each having a hole adapted to register with one another at the axially extended position of the movable end of the spring, said means for detachably connecting the movable end of said spring to said shaft comprising a removable pin inserted through said holes when in registry with one another for holding the spring in the extended condition thereof, said shaft being mounted in a horizontal position and said means connecting said straps comprising a crosspiece disposed above said shaft for slidably supporting said pulleys for movement along said shaft.

2. The combination set forth in claim 1 including a piece of relatively soft, lubricant-impregnated material aifixed to said crosspiece and interposed between said crosspiece and said shaft so as to at least partially surround said shaft.

3. A counterbalancing mechanism for use with an overhead door comprising a rigid shaft, first and second mounting brackets connected to said shaft for supporting the opposite ends of said shaft, an extension coil spring wound in spaced relation around said shaft and axially extendable therealong between said brackets, means fixably connecting one end of said spring to said shaft adjacent one end thereof, the other end of said spring being movable along said shaft, means for releasably interconnecting said shaft with the movable end of said spring when said spring is axially stressed by movement of said movable end to an extended position thereof to thereby maintain said spring in stressed condition and means connected to said movable end of said spring for coupling the same to the door so that said spring is stressed by movement of the door to thereby counterbalance the door, said first bracket having a portion defining an opening, said one end of said shaft extending through said bracket via said opening, said first-mentioned means comprising a generally 'U-shaped clip having a pair of bent-back arms engaging a convolution of said spring adjacent the fixed end thereof on opposite sides of said shaft, said clip extending through said bracket via said opening and across said one end of said shaft so as to be held in place by the tension of said spring and by engagement with said portion of said bracket.

4. The combination set forth in claim 3 including a plate curved generally complemental to the outside diameter of said spring and extending therealong from said first bracket towards the movable end of said spring, said plate and said bracket having tab and slot means interconnecting said plate and bracket to retain said plate against movement towards the movable end of said spring, said plate having a series of transverse recesses spaced axially therealong on the side thereof remote from said spring, clamp means adapted to straddle said plate and said spring in engaging relation with one of said recesses such that said clamp means is held against movement along said plate, said clamp means having a crosspiece adjustably fastened thereto for engaging the spring on the opposite side thereof from said plate to thereby deadhead the convolutions of said spring disposed axially between said crosspiece and the fixed end of said spring.

5. In combination a structure having a door opening, an overhead type door, means supporting said door for movement with respect to the door opening between a raised open position and a lowered closed position, first and second spaced brackets mounted on said structure, a shaft extending from said first bracket to said second bracket, means connecting said shaft to said brackets such that said brackets support said shaft and said shaft prevents movement of said brackets towards one another, an extension coil spring encircling said shaft between said brackets with one end of said spring fixably connected to said shaft and the other end of said spring movable axially along said shaft between first and second positions corresponding to contracted and extended conditions of said spring, means operably interconnecting the movable end of said spring with said door such that said spring so extends and contracts in response to closing and opening movement of the door to thereby provide counterbalancing force for the door, spring rate adjusting means comprising a member fixably connected to said shaft and extending adjacent and exterior to said fixed end of said spring parallel to said shaft towards the movable end of said spring and a clamp encircling and interengaging said spring and .said member, said clamp being disengageable from said member and spring for movement therealong to any selected one of a series of predetermined points for deadheading the convolutions of said spring disposed between the fixed end thereof and said clamp, said member comprising a plate curved generally complemental to the outside diameter of said spring and adapted to partially surround said spring, said plate having a series of alternating ridges and recesses extending transversely thereof and spaced axially therealong, said clamp comprising a member shaped to straddle said plate and said spring and having a center portion fitting in any one of said recesses, said ridges adjacent said one recess holding said clamp member against movement axially of said plate, said clamp member having a pair of arms extending from said center portion thereof on opposite sides of said spring, and means disposed on the opposite side of said spring from said plate and adjustably fastened to said arm and engaging said spring to thereby deadhead the convolutions thereof disposed between said engaging means and the fixed end of said spring.

6. A counterbalancing mechanism for use in balancing the weight of an overhead door supported for vertical movement to open and close a doorway in a structure, said counterbalancing mechanism comprising a rigid shaft, mounting means connected to the shaft for fixably supporting said shaft on said structure, a tension coil spring encircling said shaft between said mounting means and having one end thereof fixed to said shaft and the other end thereof movable along said shaft in the normal operating condition of said mechanism, means connected to said movable end of said spring adapted for operably connecting said spring to the door such that closing and opening movement of the door respectively causes said spring to axially extend and contract along said shaft to thereby counterbalance the door, and means detachably connecting the movable end of said spring to said shaft at a predetermined point therealong such that said spring is axially extended to thereby pre-stress said spring to facilitate connection thereof with the door, said means connected to said movable end of said spring comprising a pair of generally U-shaped straps disposed on opposite sides of said shaft and hooked through the associated side of said spring between a pair of convolutions thereof so as to engage said spring adjacent the movable end thereof, said straps each having a pair of arms extending beyond the movable end of said spring, first and second pulleys connected to and journalled respectively between said arms of said straps and means connected to said straps and extending therebetween transversely to said shaft, said last-mentioned means and said shaft each having a hole adapted to register with one another at the axially extended position of the movable end of the spring, said means for detachably connecting the movable end of said spring to said shaft comprising a removable pin inserted through said holes when in registry with one another for holding the spring in the extended condition thereof.

7. In combination a structure having a door opening, an overhead type door, means supporting said door for movement with respect to the door opening between a raised open position and a lowered closed position, first and second spaced brackets mounted on said structure, a shaft extending from said first bracket to said second bracket, means connecting said shaft to said brackets such that said brackets support said shaft and said shaft prevents movement of said brackets towards one another, an extension coil spring encircling said shaft between said brackets with one end of said spring fixably connected to said shaft and the other end of said spring movable axially along said shaft between first and second positions corresponding to contracted and extended conditions of said spring, means operably interconnecting the movable end of said spring with said door such that said spring so extends and contracts in response to closing and opening movement of the door to thereby provide counterbalancing force for the door, said shaft being disposed generally horizontally and having a vertical hole therethrough adjacent the second position of said movable end of said spring, and locking means for detachably connecting the movable end of said spring to said shaft at the second position of said movable end to thereby pre-stress said spring to facilitate connection thereof with the door when the same is in the lowered position thereof, said locking means comprising a pin slidably inserted in said shaft hole and engaged by said means operably interconnecting the movable end of the spring with the door such that the spring force exerted via said last-mentioned means on said pin binds said pin in said hole to retain the movable end of the spring fixed in said second position, said pin being free to disengage said last-mentioned means and to fall free from said shaft when the spring force exerted on said pin is relieved as a result of connecting the spring for operating the door.

8. In combination, a structure having a door opening, an overhead type door, means supporting said door for movement with respect to the door opening between a raised open position and a lowered closed position, first and second spaced brackets mounted on said structure, a rigid shaft extending from said said first bracket to said second bracket, means connecting said shaft to said brackets such that said brackets support said shaft and said shaft prevents movement of said brackets towards one another, an extension tension coil spring encirling said shaft between said brackets with one end of said spring operably connected in fixed relation to said shaft adjacent said first bracket and the other end of said spring movable axially along said shaft between first and second positions corresponding to contracted and extended conditions of said spring, a flexible element having a threaded connector attached to one end thereof threadably aflixed to said second bracket and having the other end thereof connected to the door, a pulley operably connected to the movable end of said spring for movement therewith, said element being trained over said pulley intermediate the ends of said element, and a second pulley operably supported by said shaft relative to said first bracket for guiding the running portions of said flexible element to said first pulley, and locking means for releasbly connecting the movable end of said spring to said shaft at the second position of said movable end of said spring to thereby pre-stress said spring to facilitate connection thereof with the door when the same is in the lowered position thereof, said locking means including means held in locked engagement with the shaft by the force exerted by said spring when in the pre-stressed condition thereof, said locking means being releasable by connecting said flexible element in the above-defined manner and by tensioning said flexible element by adjusting said threaded connector to thereby transfer the spring force from said locking means to said flexible element.

9. A counterbalance mechanism comprising first and second spaced brackets adapted for mounting on a structure, a shaft extending from said first bracket to said second bracket, means connecting said shaft to said brackets such that said brackets support said shaft and said shaft prevents movement of said brackets towards one another, an extension coil spring encircling said shaft between said brackets with one end of said spring operably connected in fixed relation to said shaft and the other end of said spring movable axially along said shaft between first and second positions corresponding to contracted and extended conditions of said spring, means operably interconnecting the movable end of said spring with an object to be counterbalanced thereby such that said spring so extends and contracts in response to movement of the object to thereby provide counterbalancing force for the object, a plate interconnected in fixed relation to said shaft and being curved generally complemental to the outside diameter of said spring, said plate extending adjacent and exteriorly to said fixed end of said spring parallel to said shaft towards the movable end of said spring, said plate having a series of longitudinally spaced and transversely extending abutment means therealong, and a clamp structure encircling and interengaging said spring and said plate, said clamp having a generally U-shaped member adapted to selectively engage any one of said abutment means of said plate for in fixed relation to said shaft adjacent said first bracket,

the other end of said spring being movable axially of said shaft between extended and contracted positions of the spring, said brackets extending transversely from said shaft a distance sufficient to serve as stops for containing said spring on said shaft between said brackets in the event of spring breakage, a flexible element having a threaded connector attached to one end thereof threadably aflixed to said second bracket and having the other end thereof adapted for connection to an object to be counterbalanced, a pulley operably connected to said movable end of said spring for movement therewith, an axle operably supported by said shaft relative to said first bracket and extending transversely of said shaft beyond the movable end of said spring, a second pulley journalled on said axle, said flexible element running from said one end thereof over said first pulley and back to and over said second pulley so that said spring extends and contracts axially along said shaft in response to force applied to the other end of said flexible element to thereby provide a counterbalancing reaction force thereto, and locking means for releasably connecting the movable end of said spring to said shaft at said extended position of said movable end of said spring to thereby prestress said spring to facilitate connection thereof via said flexible element with the object to be counterbalanced, said locking means including means held in locked engagement with the shaft by the force exerted by said spring when in the pre-stressed condition thereof, said locking means being releasable by interconnecting said flexible element in the above-defined manner between said second bracket and the object to be counterbalanced and by tensioning said flexible element by adjusting said threaded connector to thereby transfer the spring force from said locking means to said flexible element.

References Cited in the file of this patent UNITED STATES PATENTS 748,641 Newell Jan. 5, 1904 2,041,221 Brunst May 19, 1936 2,139,383 Robinson Dec. 6, 1938 2,259,979 Norberg Oct. 21, 1941 2,311,703 Shwonen et al Feb. 23, 1943 2,702,082 Wolf Feb. 15, 1955 2,894,572 Nelson July 14, 1959 

1. A COUNTERBALANCING MECHANISM FOR USE IN BALANCING THE WEIGHT OF AN OVERHEAD DOOR SUPPORTED FOR VERTICAL MOVEMENT TO OPEN AND CLOSE A DOORWAY IN A STRUCTURE, SAID COUNTERBALANCING MECHANISM COMPRISING A RIGID SHAFT, MOUNTING MEANS CONNECTED TO THE SHAFT FOR FIXABLY SUPPORTING SAID SHAFT ON SAID STRUCTURE, A TENSION COIL SPRING ENCIRCLING SAID SHAFT BETWEEN SAID MOUNTING MEANS AND HAVING ONE END THEREOF FIXED TO SAID SHAFT AND THE OTHER END THEREOF MOVABLE ALONG SAID SHAFT IN THE NORMAL OPERATING CONDITION OF SAID MECHANISM, MEANS CONNECTED TO SAID MOVABLE END OF SAID SPRING ADAPTED FOR OPERABLY CONNECTING SAID SPRING TO THE DOOR SUCH THAT CLOSING AND OPENING MOVEMENT OF THE DOOR RESPECTIVELY CAUSES SAID SPRING TO AXIALLY EXTEND AND CONTRACT ALONG SAID SHAFT TO THEREBY COUNTERBALANCE THE DOOR, AND MEANS DETACHABLY CONNECTING THE MOVABLE END OF SAID SPRING TO SAID SHAFT AT A PREDETERMINED POINT THEREALONG SUCH THAT SAID SPRING IS AXIALLY EXTENDED TO THEREBY PRESTRESS SAID SPRING TO FACILITATE CONNECTION THEREOF WITH THE DOOR, SAID MEANS CONNECTED TO SAID MOVABLE END OF SAID SPRING COMPRISING A PAIR OF GENERALLY U-SHAPED STRAPS DISPOSED ON OP- 